[1.7.3] Community Delta-V Map 2.7

[Kowgan]

Glad to be of help.

Wiki is having migration issues (for a few months now, go figure), and as such, the "Upload New Files" function is broken. Once it gets fixed, I'll make sure to update the chart there.

[Mat2ch]

Your dV map is a big help!

I didn't notice the problems with the wiki. Well, I'll start a nag thread somewhere Squad will see it

[Anglave]

Based on personal experience in 1.0.4, Laythe surface-to-orbit is more like 3400 ÃŽâ€v, rather than the 2600 listed here and on the Wiki.

Check this thread for more detail.

[Kowgan]

@Anglave: After reading your thread, I think you just lack of enough TWR to make it to orbit without spending too much near sea-level. Can you fill your lander up to 3200dV and make it to orbit in Kerbin?

[Northstar1989]

Something looks fishy about the Delta-V figures for returns (at least using the method you said to calculate returns- i.e. using the Eeloo example). It should never take more Delta-V to get a return-trajectory than it took to capture from the inbound trajectory in the first place, when returning from any body further out from the Sun/Kerbin than the departure point. I.e. it never takes less Delta-V to circularize an orbit with a higher apoapsis from the sun (essentially what you are doing when you capture at a planet further out than Kerbin) than it does to drop the periapsis back down to where it was before...

Are you sure you're basing the calculations on the most efficient returns- i.e. burning within the SOI of a planet/moon so that you escape with a trajectory retrograde relative the the planet/moon's movement about the Sun/Kerbin? (when Kerbin is in the correct position for a return if going from planet to planet)

Regards,

Northstar

[Superfluous J]

Are you sure you're basing the calculations on the most efficient returns- i.e. burning within the SOI of a planet/moon so that you escape with a trajectory retrograde relative the the planet/moon's movement about the Sun/Kerbin? (when Kerbin is in the correct position for a return if going from planet to planet)

Based on the text in the upper right (About how flight times were based on AlexMoon's calculator) I'd assume - with no further info to the contrary - that the dV requirements were arrived at similarly. No guarantee, of course, but it makes sense.

And if it doesn't do that, why doesn't it? How were the numbers derived? Was each transfer burn on the chart planned for all situations?

Regarding Eeloo, based on this chart I expect to orbit it from LKO would take 950+1140+1370 or 3460, plus somewhere between 0 and 1330 for the plane change. Returning to Kerbin from LEO would take 1370+1140 or 2510, plus somewhere between 0 and 1330 for the plane change (probably on the much lower end). I assume you're not reading the chart that way because the return trip takes 950 or better LESS dV than the outbound trip in this case.

[Anglave]

@Anglave: After reading your thread, I think you just lack of enough TWR to make it to orbit without spending too much near sea-level. Can you fill your lander up to 3200dV and make it to orbit in Kerbin?

I concede it's possible that a combination of gravity losses (due to low TWR) and aerodynamic losses (due to my lander's pancake shape) have increased my effective ÃŽâ€v requirement. I'll certainly do some more testing.

Testing the existing lander design on Kerbin isn't going to be very meaningful, as Laythe has only 80% the gravity of Kerbin. The lander's TWR on Kerbin would definitely be too low. I am, however, inspired to run some more tests from Laythe, with a higher TWR or more aerodynamic shape.

[RocketBlam]

I don't know how you came to 6000 D/v for Eve... I just tried it with that, and the highest I got was an Apo of 38k.

[jjansen]

Awesome work, I use this chart (and the prior versions) all the time, for nearly every launch.

Keep it updated but otherwise, don't change a thing about its style (though, perhaps dV for return trips?? Maybe an addenda web that shows minimum dV expectable for a porkchop plot selection?)

Whatever you do, the circle representing Jool ought to become either a skull or a Kraken icon.

Again, great work!

[Galahir950]

Do you mean you tried to lift off from Eve with 6000 D/v? The 6000 is for going from a Low Eve Orbit to the surface, which would require less since the atmosphere would slow you down. I believe that trying to leave Eve's Surface is similar except you are fighting gravity and the atmosphere to leave Eve's thick atmosphere.

Edited July 19, 2015 by Galahir950

[RocketBlam]

Do you mean you tried to lift off from Eve with 6000 D/v? The 6000 is for going from a Low Eve Orbit to the surface, which would require less since the atmosphere would slow you down. I believe that trying to leave Eve's Surface is similar except you are fighting gravity and the atmosphere to leave Eve's thick atmosphere.

Uh, going from low Eve orbit to the surface takes about 200 D/V... the D/V it takes to put your Peri below the atmosphere line.

[Galahir950]

I think the 6000 D/v is for getting the periapsis to 0, no aerobrakes, and keeping the craft slow enough not to burn up in the thick atmosphere. You would have to ask Kowgan for clarification.

[RocketBlam]

That seems like an odd assumption to me. I don't know anyone who would land on a planet with an atmosphere, let alone Eve, using engines. The measurement for what D/V it takes to get to orbit from the surface seems much more useful.

Edited July 19, 2015 by RocketBlam

[Galahir950]

That seems like an odd assumption to me. I don't know anyone who would land on a planet with an atmosphere, let alone Eve, using engines. The measurement for what D/V it takes to get to orbit from the surface seems much more useful.

I know it is an odd assumption, I am just trying to find an explanation that matches the numbers. I do not know exactly how Kowgan does his calculations, I only do the summaries for the summary version.

[Kowgan]

Numbers between checkpoints are the needed dV to move from Checkpoint A to Checkpoint B. Or from Checkpoint B to Checkpoint A. No matter what way.

6000m/s is the required value to lift off from Eve sea level up to a circular Low Eve Orbit at 100km, just like the map shows you. The same value is needed to land on Eve from Low Eve Orbit, if you don't use aerobraking/parachutes. Since Eve has an atmosphere, aerobraking is compulsory. Of course, all my tests are made with aerodynamic-friendly vessels, so, ALL the values on the map are designed for optimistic scenarios. If you're trying to fly a brick, you should count for that on the dV usage.

I'm really trying to make the "how-to-use this map" as clear as possible. The OP have more detailed instructions for closer understanding, but either I'm failing hard to express myself, or people are simply not reading it.

@jjansen: Thank you.

As I explained above, the return values are usually the same as the original trip itself. Values to move from A to B are the same to move from B to A, unless you use aerobraking.

Porkchop plots are available on Alexmoon's github, and the values on the map expect you to use a proper transfer window to transfer burn. I don't know how would I put a porkchop view directly on the map.

As for the Jool icon, do you mean Galahir's version? Or the Space Walrus sitting there, vigilant?

Edited July 20, 2015 by Kowgan

[RocketBlam]

6000m/s is the required value to lift off from Eve sea level up to a circular Low Eve Orbit at 100km, just like the map shows you.

Can you post a vessel that can do this? Because my experience is that even with a vessel taking off from above sea level, 6K D/V doesn't get you out of the atmosphere, let alone into orbit.

[RocketBlam]

For example, I've been trying to get this off of Eve. It has 6500 D/V, and a solid TWR ratio through the flight, and yet it still cannot achieve orbit even from 3,700 meters.

My guess is it would take at least 7,500 D/V from 3,700 meters, and probably more like 9,000-10,000 from sea level.

[Superfluous J]

I've not launched from Eve yet, but those struts, fuel lines, and open docking port look like they may cause a decent bit of drag. Not to mention the landing legs and girders. I have a feeling Eve is MUCH more drag-sensitive than Kerbin or any other world. Except maybe Jool, but you can't ascend from the surface to orbit on Jool...

[RocketBlam]

It is more drag sensitive, for sure. Two of the landing legs/girders are gone within 11 seconds though, before drag really might become an issue, since they're connected to an asparagus stage that gets jettisoned.

I may try it with a more steamlined vessel for giggles.

[Galahir950]

Numbers between checkpoints are the needed dV to move from Checkpoint A to Checkpoint B. Or from Checkpoint B to Checkpoint A. No matter what way.

6000m/s is the required value to lift off from Eve sea level up to a circular Low Eve Orbit at 100km, just like the map shows you. The same value is needed to land on Eve from Low Eve Orbit, if you don't use aerobraking/parachutes. Since Eve has an atmosphere, aerobraking is compulsory.

Thank you for clarifying this, it helped clear up some questions I had about the chart.

[Kowgan]

@RocketBlam: Your ship has 6500m/s of vacuum Delta-V, not atmospheric.

The problem with taking off from Eve is having a vessel with enough fuel to carry about 4000~5000m/s of atmospheric delta-V, and at the same time, having enough TWR. This vessel will most likely be huuuge.

[Superfluous J]

@RocketBlam: Your ship has 6500m/s of vacuum Delta-V, not atmospheric.

The problem with taking off from Eve is having a vessel with enough fuel to carry about 4000~5000m/s of atmospheric delta-V, and at the same time, having enough TWR. This vessel will most likely be huuuge.

Traditionally these charts list vacuum dV, knowing that atmo dV will be less and assuming the player will chose reasonable engines. If this chart does not do that and instead assumes atmo dV for atmo bodies, it should make that clear.

That would also explain 3200dV off of Kerbin. My absolute best I've ever done was about 3300 (vacuum) dV.

[Kowgan]

As explained in the chart itself, the values shown there are a mix of atmospheric and vacuum delta-V.

If there's a demand for following the tradition, I'll gladly change all the values for vacuum dV only. For all other personal preferences, anyone can download and edit the master file available in the OP, and have their own custom chart.

[RocketBlam]

The problem, I hope you can see, is that people have no idea what "mix" you are using, so they can't rely on the numbers. I mean, the chart says 6k d/V, but then you say you need a vessel with 4-5k of atmospheric D/V. Nobody can tell how you came up with the numbers, or what the mix is supposed to be, so the numbers aren't useful for predicting how much D/V you will need, which is the point in the first place.

[Galahir950]

Nobody can tell how you came up with the numbers, or what the mix is supposed to be, so the numbers aren't useful for predicting how much D/V you will need

I also think iris a bit hard to figure out what is necessary. Even after I read the explanation, I still use the planetary values as all atmospheric, so I have 3200 m/s of atmospheric D/v on the Kerbin lifters.